Doc onFailureWithBackoff (#28356)
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Christopher Batey
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3 changed files with 238 additions and 5 deletions
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@ -14,11 +14,50 @@ Wrap the given @apidoc[Source] with a @apidoc[Source] that will restart it when
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## Description
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This @apidoc[Source] will never emit a failure, since the failure of the wrapped @apidoc[Source] is always handled by
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restarting. The wrapped @apidoc[Source] can be cancelled by cancelling this @apidoc[Source].
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When that happens, the wrapped @apidoc[Source], if currently running will be cancelled, and it will not be restarted.
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This can be triggered simply by the downstream cancelling, or externally by introducing a @apidoc[KillSwitch] right
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after this @apidoc[Source] in the graph.
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Wraps the given @apidoc[Source] with a @apidoc[Source] that will restart it when it fails using an exponential backoff.
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The backoff resets back to `minBackoff` if there hasn't been a failure within `minBackoff`.
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This @apidoc[Source] will never emit a failure, since the failure of the wrapped @apidoc[Source] is always handled by
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restarting. The wrapped @apidoc[Source] can be completed by completing this @apidoc[Source].
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When that happens, the wrapped @apidoc[Source], if currently running will be cancelled, and it will not be restarted.
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This can be triggered by the downstream cancelling, or externally by introducing a @ref[KillSwitch](../../stream-dynamic.md#controlling-stream-completion-with-killswitch) right
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after this @apidoc[Source] in the graph.
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See also:
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* @ref:[RestartFlow.onFailuresWithBackoff](../RestartFlow/onFailuresWithBackoff.md)
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* @ref:[RestartFlow.withBackoff](../RestartFlow/withBackoff.md)
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* @ref:[RestartSink.withBackoff](../RestartSink/withBackoff.md)
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## Examples
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This shows that a Source is not restarted if it completes, only if it fails. Tick is only printed
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three times as the `take(3)` means the inner source completes successfully after emitting the first 3 elements.
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Scala
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: @@snip [Restart.scala](/akka-docs/src/test/scala/docs/stream/operators/source/Restart.scala) { #restart-failure-inner-complete }
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Java
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: @@snip [Restart.java](/akka-docs/src/test/java/jdocs/stream/operators/source/Restart.java) { #restart-failure-inner-complete }
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If the inner source instead fails, it will be restarted with an increasing backoff. The source emits 1, 2, 3, and then throws an exception.
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The first time the exception is thrown the source is restarted after 1s, then 2s etc, until the `maxBackoff` of 10s.
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Scala
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: @@snip [Restart.scala](/akka-docs/src/test/scala/docs/stream/operators/source/Restart.scala) { #restart-failure-inner-failure }
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Java
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: @@snip [Restart.java](/akka-docs/src/test/java/jdocs/stream/operators/source/Restart.java) { #restart-failure-inner-failure }
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Finally, to be able to stop the restarting, a kill switch can be used. The kill switch is inserted right after the restart
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source. The inner source is the same as above so emits 3 elements and then fails. A killswitch is used to be able to stop the source
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being restarted:
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Scala
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: @@snip [Restart.scala](/akka-docs/src/test/scala/docs/stream/operators/source/Restart.scala) { #restart-failure-inner-complete-kill-switch }
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Java
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: @@snip [Restart.java](/akka-docs/src/test/java/jdocs/stream/operators/source/Restart.java) { #restart-failure-inner-complete-kill-switch }
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## Reactive Streams semantics
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@ -0,0 +1,111 @@
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/*
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* Copyright (C) 2019-2020 Lightbend Inc. <https://www.lightbend.com>
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*/
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package jdocs.stream.operators.source;
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import akka.NotUsed;
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import akka.actor.Cancellable;
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import akka.japi.Creator;
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import akka.stream.KillSwitches;
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import akka.stream.UniqueKillSwitch;
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import akka.stream.javadsl.Keep;
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import akka.stream.javadsl.RestartSource;
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import akka.stream.javadsl.Sink;
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import akka.stream.javadsl.Source;
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import java.time.Duration;
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import java.util.Arrays;
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public class Restart {
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static akka.actor.ActorSystem system = akka.actor.ActorSystem.create();
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public static void onRestartWithBackoffInnerFailure() {
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// #restart-failure-inner-failure
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// could throw if for example it used a database connection to get rows
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Source<Creator<Integer>, NotUsed> flakySource =
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Source.from(
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Arrays.<Creator<Integer>>asList(
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() -> 1,
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() -> 2,
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() -> 3,
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() -> {
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throw new RuntimeException("darn");
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}));
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Source<Creator<Integer>, NotUsed> forever =
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RestartSource.onFailuresWithBackoff(
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Duration.ofSeconds(1), Duration.ofSeconds(10), 0.1, () -> flakySource);
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forever.runWith(
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Sink.foreach((Creator<Integer> nr) -> system.log().info("{}", nr.create())), system);
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// logs
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// [INFO] [12/10/2019 13:51:58.300] [default-akka.test.stream-dispatcher-7]
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// [akka.actor.ActorSystemImpl(default)] 1
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// [INFO] [12/10/2019 13:51:58.301] [default-akka.test.stream-dispatcher-7]
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// [akka.actor.ActorSystemImpl(default)] 2
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// [INFO] [12/10/2019 13:51:58.302] [default-akka.test.stream-dispatcher-7]
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// [akka.actor.ActorSystemImpl(default)] 3
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// [WARN] [12/10/2019 13:51:58.310] [default-akka.test.stream-dispatcher-7]
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// [RestartWithBackoffSource(akka://default)] Restarting graph due to failure. stack_trace:
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// (RuntimeException: darn)
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// --> 1 second gap
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// [INFO] [12/10/2019 13:51:59.379] [default-akka.test.stream-dispatcher-8]
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// [akka.actor.ActorSystemImpl(default)] 1
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// [INFO] [12/10/2019 13:51:59.382] [default-akka.test.stream-dispatcher-8]
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// [akka.actor.ActorSystemImpl(default)] 2
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// [INFO] [12/10/2019 13:51:59.383] [default-akka.test.stream-dispatcher-8]
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// [akka.actor.ActorSystemImpl(default)] 3
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// [WARN] [12/10/2019 13:51:59.386] [default-akka.test.stream-dispatcher-8]
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// [RestartWithBackoffSource(akka://default)] Restarting graph due to failure. stack_trace:
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// (RuntimeException: darn)
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// --> 2 second gap
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// [INFO] [12/10/2019 13:52:01.594] [default-akka.test.stream-dispatcher-8]
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// [akka.actor.ActorSystemImpl(default)] 1
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// [INFO] [12/10/2019 13:52:01.595] [default-akka.test.stream-dispatcher-8]
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// [akka.actor.ActorSystemImpl(default)] 2
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// [INFO] [12/10/2019 13:52:01.595] [default-akka.test.stream-dispatcher-8]
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// [akka.actor.ActorSystemImpl(default)] 3
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// [WARN] [12/10/2019 13:52:01.596] [default-akka.test.stream-dispatcher-8]
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// [RestartWithBackoffSource(akka://default)] Restarting graph due to failure. stack_trace:
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// (RuntimeException: darn)
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// #restart-failure-inner-failure
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}
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public static void onRestartWithBackoffInnerComplete() {
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// #restart-failure-inner-complete
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Source<String, Cancellable> finiteSource =
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Source.tick(Duration.ofSeconds(1), Duration.ofSeconds(1), "tick").take(3);
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Source<String, NotUsed> forever =
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RestartSource.onFailuresWithBackoff(
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Duration.ofSeconds(1), Duration.ofSeconds(10), 0.1, () -> finiteSource);
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forever.runWith(Sink.foreach(System.out::println), system);
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// prints
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// tick
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// tick
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// tick
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// #restart-failure-inner-complete
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}
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public static void onRestartWitFailureKillSwitch() {
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// #restart-failure-inner-complete-kill-switch
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Source<Creator<Integer>, NotUsed> flakySource =
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Source.from(
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Arrays.<Creator<Integer>>asList(
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() -> 1,
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() -> 2,
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() -> 3,
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() -> {
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throw new RuntimeException("darn");
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}));
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UniqueKillSwitch stopRestarting =
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RestartSource.onFailuresWithBackoff(
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Duration.ofSeconds(1), Duration.ofSeconds(10), 0.1, () -> flakySource)
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.viaMat(KillSwitches.single(), Keep.right())
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.toMat(Sink.foreach(nr -> System.out.println("nr " + nr.create())), Keep.left())
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.run(system);
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// ... from some where else
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// stop the source from restarting
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stopRestarting.shutdown();
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// #restart-failure-inner-complete-kill-switch
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}
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}
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@ -0,0 +1,83 @@
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/*
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* Copyright (C) 2009-2020 Lightbend Inc. <https://www.lightbend.com>
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*/
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package docs.stream.operators.source
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import akka.NotUsed
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import akka.actor.ActorSystem
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import akka.stream.KillSwitches
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import akka.stream.UniqueKillSwitch
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import akka.stream.scaladsl.Keep
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import akka.stream.scaladsl.RestartSource
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import akka.stream.scaladsl.Sink
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import scala.concurrent.duration._
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import scala.util.control.NoStackTrace
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// #imports
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import akka.stream.scaladsl.Source
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// #imports
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object Restart extends App {
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implicit val system: ActorSystem = ActorSystem()
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onRestartWitFailureKillSwitch()
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case class CantConnectToDatabase(msg: String) extends RuntimeException(msg) with NoStackTrace
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def onRestartWithBackoffInnerFailure(): Unit = {
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//#restart-failure-inner-failure
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// could throw if for example it used a database connection to get rows
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val flakySource: Source[() => Int, NotUsed] =
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Source(List(() => 1, () => 2, () => 3, () => throw CantConnectToDatabase("darn")))
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val forever =
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RestartSource.onFailuresWithBackoff(minBackoff = 1.second, maxBackoff = 10.seconds, 0.1)(() => flakySource)
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forever.runWith(Sink.foreach(nr => system.log.info("{}", nr())))
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// logs
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//[INFO] [12/10/2019 13:51:58.300] [default-akka.test.stream-dispatcher-7] [akka.actor.ActorSystemImpl(default)] 1
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//[INFO] [12/10/2019 13:51:58.301] [default-akka.test.stream-dispatcher-7] [akka.actor.ActorSystemImpl(default)] 2
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//[INFO] [12/10/2019 13:51:58.302] [default-akka.test.stream-dispatcher-7] [akka.actor.ActorSystemImpl(default)] 3
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//[WARN] [12/10/2019 13:51:58.310] [default-akka.test.stream-dispatcher-7] [RestartWithBackoffSource(akka://default)] Restarting graph due to failure. stack_trace: (docs.stream.operators.source.Restart$CantConnectToDatabase: darn)
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// --> 1 second gap
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//[INFO] [12/10/2019 13:51:59.379] [default-akka.test.stream-dispatcher-8] [akka.actor.ActorSystemImpl(default)] 1
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//[INFO] [12/10/2019 13:51:59.382] [default-akka.test.stream-dispatcher-8] [akka.actor.ActorSystemImpl(default)] 2
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//[INFO] [12/10/2019 13:51:59.383] [default-akka.test.stream-dispatcher-8] [akka.actor.ActorSystemImpl(default)] 3
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//[WARN] [12/10/2019 13:51:59.386] [default-akka.test.stream-dispatcher-8] [RestartWithBackoffSource(akka://default)] Restarting graph due to failure. stack_trace: (docs.stream.operators.source.Restart$CantConnectToDatabase: darn)
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//--> 2 second gap
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//[INFO] [12/10/2019 13:52:01.594] [default-akka.test.stream-dispatcher-8] [akka.actor.ActorSystemImpl(default)] 1
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//[INFO] [12/10/2019 13:52:01.595] [default-akka.test.stream-dispatcher-8] [akka.actor.ActorSystemImpl(default)] 2
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//[INFO] [12/10/2019 13:52:01.595] [default-akka.test.stream-dispatcher-8] [akka.actor.ActorSystemImpl(default)] 3
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//[WARN] [12/10/2019 13:52:01.596] [default-akka.test.stream-dispatcher-8] [RestartWithBackoffSource(akka://default)] Restarting graph due to failure. stack_trace: (docs.stream.operators.source.Restart$CantConnectToDatabase: darn)
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//#restart-failure-inner-failure
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}
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def onRestartWithBackoffInnerComplete() {
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//#restart-failure-inner-complete
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val finiteSource = Source.tick(1.second, 1.second, "tick").take(3)
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val forever = RestartSource.onFailuresWithBackoff(1.second, 10.seconds, 0.1)(() => finiteSource)
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forever.runWith(Sink.foreach(println))
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// prints
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// tick
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// tick
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// tick
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//#restart-failure-inner-complete
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}
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def onRestartWitFailureKillSwitch(): Unit = {
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//#restart-failure-inner-complete-kill-switch
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val flakySource: Source[() => Int, NotUsed] =
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Source(List(() => 1, () => 2, () => 3, () => throw CantConnectToDatabase("darn")))
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val stopRestarting: UniqueKillSwitch =
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RestartSource
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.onFailuresWithBackoff(1.second, 10.seconds, 0.1)(() => flakySource)
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.viaMat(KillSwitches.single)(Keep.right)
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.toMat(Sink.foreach(nr => println(s"Nr ${nr()}")))(Keep.left)
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.run()
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//... from some where else
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// stop the source from restarting
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stopRestarting.shutdown()
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//#restart-failure-inner-complete-kill-switch
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}
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}
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